Optimal Detection of WeaknJ(1H–119Sn) Couplings by Gradient-Enhanced 1D and 2D Heteronuclear Multiple-Quantum Correlation Spectroscopy. Application to a Novel Tin Derivative of Erythromycin A
✍ Scribed by José C. Martins; François Kayser; Patricia Verheyden; Marcel Gielen; Rudolph Willem; Monique Biesemans
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 114 KB
- Volume
- 124
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Over the past years, organotin chemistry has enjoyed in-tion of weak n J( 1 H-119 Sn) scalar couplings is one of the tools which can provide information on weak intramolecular creasing interest as a source of new compounds with potential applications both in biomedicine (1) and in material coordinations involving tin. Unfortunately, these couplings are hardly measurable either from standard 1D 1 H spectra, sciences (2). As a result, there is a growing need for their fine-tuned structural characterization. To this end, high-reso-the coupling satellites being hidden in the foot of the parent 1 H resonance, or from 119 Sn spectra, because of the usual lution NMR provides powerful 1 H-{ 1 H} and 1 H-{ 13 C} correlation techniques (3), which can be supplemented by 1D large linewidth of the 119 Sn resonances.
To address these problems, we have recently introduced 119 Sn NMR. Whereas their combined use furnishes a wealth of structural and conformational information as to the or-1D and 2D 1 H-{ 119 Sn} HMQC spectroscopy (10, 11). In our hands, this novel tool has proved essential for gaining ganic moieties in these compounds, they generally underperform as far as the characteristics of their tin atom(s) are fine structural features in a variety of organotin compounds (12)(13)(14). While 119 Sn has a more favorable natural abun-concerned.
Although it is a main-group element, its location in the dance than 13 C (8.7 vs 1.1%), subtraction artifacts originating from phase cycling generate t 1 noise bands at the fre-fifth period implies that the tin atom has both a highly polarizable valence-electron shell and empty 5d orbitals facilitat-quency of intense resonances from, for instance, tert-butyl or phenyl moieties. This hampers the reliable observation of ing coordination extension (4). This high coordination variability, which extends typically from coordination four to n J( 1 H-119 Sn) scalar-coupling correlations with low intensity. This report presents and discusses the successful impleseven for organotin(IV) compounds, is reflected by the frementation of pulsed field gradients (PFGs) in order to overquent existence of intramolecular donor-acceptor interaccome this dynamic-range-related drawback. The superior tions involving the tin atom as a Lewis acid (4). These performance of the gradient-enhanced scheme and its impact interactions often lie at the frontier of real covalent bonds on the structural characterization of bio-organotin comand strong van der Waals interactions, being characterized pounds are demonstrated with Ery(OSn(tBu) 2 ) 2 O, a novel by bond lengths ranging from 2.4 to 3.2 A ˚(5, 6). As a derivative of the antibiotic erythromycin A (further repreconsequence, while readily observable in the solid state by sented as Ery(OH) 2 ), currently under our investigation. X-ray diffraction techniques, hypervalent organotin com-Usually, three PFGs are incorporated into the basic pounds being often crystallization friendly (5, 6), such intra-HMQC pulse sequence to achieve the desired coherencemolecular coordinations are sometimes difficult to demonpathway selection (15, 16) (Fig. 1). Two PFGs symmetristrate in solution. Doing so, however, is essential, because cally sandwich the p( 1 H) pulse in the center of the t 1 evoluthe same organotin compound can display different coordition period and the third immediately follows the last heteronation features and, henceforth, different structures in the nuclear p/2 ( n X) pulse. The coherence-transfer pathways solid and solution states (5-7).
leading to the desired correlations, described by single-shift-Although helpful, 119 Sn chemical-shift data are usually not transition operators (17), are shown in Fig. 1. After the sufficient to characterize the compounds (8, 9). The detecpreparation period, tuned to the n J( 1 H-119 Sn) couplings of interest, the first p/2( n X) pulse creates zero-and double- † To whom correspondence should be addressed.